A) Field of the Invention
The present invention relates generally to a micro pattern forming method and a semiconductor device manufacturing method, and more particularly to a method of forming a micro pattern by forming a photosensitive resist film on an antireflection film and exposing and developing the resist film, and to a method of manufacturing a semiconductor device using micro patterns.
B) Description of the Related Art
With reference to FIGS. 3A to 3C, description will be given on a method of forming a copper wiring line by using a conventional dual damascene method.
As shown in FIG. 3A, copper wiring lines 101 are formed in wiring grooves formed in a surface layer of an interlayer insulating film 100 on a semiconductor substrate. On this interlayer insulating film 100, a diffusion preventing film 102 is formed to prevent diffusion of copper. On this diffusion preventing film 102, an interlayer insulating film 103, an etching stopper film 104, an interlayer insulating film 105 and an antireflection film 106 are stacked in this order. A resist film 107 is formed on the antireflection film 106. The resist film 107 is exposed and developed to form an opening 107a corresponding to a via hole.
As the material of the antireflection film 106, material having an attenuation coefficient k larger than 1 is used. This antireflection film mitigates the influence of a variation in reflection amounts of exposure light from the underlying film, so that the resist film 107 can be patterned with good controllability.
As shown in FIG. 3B, by using the resist film 107 as a mask, the films from the antireflection film 106 to the bottom of the interlayer film 103 are etched to form a via hole 110.
As shown in FIG. 3C, after the resist film 107 is removed, a wiring groove is formed reaching the upper surface of the etching stopper film 104. The diffusion preventing film 102 left on the bottom of the via hole 110 is removed to expose the copper wiring line 101. The wiring groove and via hole 110 is filled in with copper to form a copper wiring pattern.
If the diameter of the via hole 110 is 0.3 μm or larger, the via hole 110 can be formed by the above-described processes. However, if the diameter of the via hole 110 is smaller than 0.3 μm, a micro opening for the via hole is difficult to be formed due to a standing wave generated in the resist film 107.
With reference to FIGS. 4A and 4B, an exposure method will be described which is disclosed in Japanese Patent Laid-open Publication No. 2000-195791. The structure from an interlayer insulating film 100 to an antireflection film 106 shown in FIG. 4A is the same as that shown in FIG. 3A. In the conventional structure shown in FIG. 4A, a second antireflection film 120 is formed on the antireflection film 106. As shown in FIG. 4B, a resist film 121 is formed on the second antireflection film 120, exposed and developed.
The first antireflection film 106 is used in an absorption mode. In the absorption mode, exposure light is absorbed so that light scattered by the resist film can be reduced and undesired exposure can be avoided.
The second antireflection film 120 is used in a countervailing interference mode. In the countervailing interference mode, the phase of light reflected on the bottom of an antireflection film is shifted from the phase of light reflected on the top of the antireflection film, so that reflected light returning to the resist film can be reduced.
A lamination of an antireflection film used in the absorption mode and an antireflection film used in the countervailing interference mode can reduce reflected light returning to the resist film, allowing to form a micro pattern.
The related art is published in the JP-A-2000-195791.
In a practical production process, an opening having a desired size is not always formed through patterning a resist film. If the size of an opening after development is different from a design value, the resist film is removed by ashing and resist is again coated.
While the resist film is ashed, the surface layer of the second antireflection film 120 is decomposed by oxidation and the like. As the surface layer of the antireflection film 120 is decomposed, it is not possible to have desired reflectivity lowering effects. An optimum exposure amount becomes different from a design value.